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Department Environmental Toxicology

How do aquatic organisms respond to stress?

We investigate how freshwater organisms respond to chemical exposure and other stressors in their environment. In particular, we explore adaptive and toxicological response pathways and develop conceptual and computational models to support knowledge-based risk assessment.

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A study just published by Eawag scientists shows that gold and silver each amounting to around CHF 1.5 million a year are lost via effluents and sludge from wastewater treatment plants in Switzerland. The concentrations measured do not pose risks to the environment – and recycling would not be economically worthwhile. However, the study also produced surprising findings on other trace elements in wastewater, including rare earth metals such as gadolinium and the heavy metal niobium. Read more

Single-celled bacteria are capable of mixing water layers in lakes – not directly, by movement of their flagella, but by accumulating locally and thus increasing water density. The heavier water then sinks, creating circular currents. Researchers have now observed this process for the first time not just in the laboratory, but in a natural water body – Lake Cadagno (canton of Ticino). Read more

Latest Publications

Permanent fish cell lines constitute a promising complement or substitute for fish in the environmental risk assessment of chemicals. We demonstrate the potential of a set of cell lines originating from rainbow trout (Oncorhynchus mykiss) to aid in the prediction of chemical bioaccumulation in fish, using benzo[a]pyrene (BaP) as a model chemical. We selected three cell lines from different tissues to more fully account for whole-body biotransformation in vivo: the RTL-W1 cell line, representing the liver as major site of biotransformation, and the RTgill-W1 (gill) and RTgutGC (intestine) cell lines, as important environment-organism interfaces, which likely influence chemical uptake. All three cell lines were found to effectively biotransform BaP. However, rates of in vitro clearance differed, with the RTL-W1 cell line being most efficient, followed by RTgutGC. Co-exposures with α-naphthoflavone as potent inhibitor of biotransformation, assessment of CYP1A catalytic activity, and the progression of cellular toxicity upon prolonged BaP exposure revealed that BaP is handled differently in the RTgill-W1 compared to the other two cell lines. Application of the cell-line-derived in vitro clearance rates into a physiology-based toxicokinetic model predicted a BaP bioconcentration factor (BCF) of 909-1057 compared to 920 reported for rainbow trout in vivo.

Uptake and effects of cerium(III) and cerium oxide nanoparticles to Chlamydomonas reinhardtii

Cerium (Ce) and cerium oxide nanoparticles (CeO2 NP) are increasingly used in different applications. Upon their release into the aquatic environment, the exposure of aquatic organisms becomes likely. In this study, the uptake of CeO2 NP and Ce3+ into the wild type and cell wall free mutant of Chlamydomonas reinhardtii was examined upon short term exposure. Separation of CeO2 NP and Ce3+ not taken up or loosely bound to the cells was performed by washing algae with EDTA.

Despite a concentration and time dependent increase of cellular Ce upon exposure to CeO2 NP with the maximal calculated Ce concentration corresponding to 1.1 CeO2 NP per cell, an internalization of CeO2 NP with a mean size of 140 nm in C. reinhardtii was excluded. In contrast, dissolved Ce3+ (1 and 10 μM) was taken up both in the wild type and cell wall free mutant of C. reinhardtii, with a linear increase of cellular Ce within 1–2 h and maximal cellular Ce of 6.04 × 10−4 mol Lcell−1 (wild type) and 9.0 × 10−5 mol Lcell−1 (cell wall free mutant). Based on competition with Ca2+ for Ce3+ uptake, on the comparison of the wild type and the cell wall free mutant and on inhibition of photosynthetic yield, we suggest that no efficient uptake routes for Ce3+ are available in C. reinhardtii and that a fraction of the cellular Ce in the wild type strongly sorbs to the algal cell wall.

Glutathione S-transferase protein expression in different life stages of zebrafish (Danio rerio)

Zebrafish is a widely used animal model in biomedical sciences and toxicology. Although evidence for the presence of phases I and II xenobiotic defense mechanisms in zebrafish exists on the transcriptional and enzyme activity level, little is known about the protein expression of xenobiotic metabolizing enzymes. Given the important role of glutathione S-transferases (GSTs) in phase II biotransformation, we analyzed cytosolic GST proteins in zebrafish early life stages and different organs of adult male and female fish, using a targeted proteomics approach. The established multiple reaction monitoring-based assays enable the measurement of the relative abundance of specific GST isoenzymes and GST classes in zebrafish through a combination of proteotypic peptides and peptides shared within the same class. GSTs of the classes alpha, mu, pi and rho are expressed in zebrafish embryo as early as 4 h postfertilization (hpf). The majority of GST enzymes are present at 72 hpf followed by a continuous increase in expression thereafter. In adult zebrafish, GST expression is organ dependent, with most of the GST classes showing the highest expression in the liver. The expression of a wide range of cytosolic GST isoenzymes and classes in zebrafish early life stages and adulthood supports the use of zebrafish as a model organism in chemical-related investigations.

Green algae and networks for adverse outcome pathways

If adverse outcome pathways (AOPs) are to become the new standard predictive tool for chemical risk assessment in ecotoxicology, substantial effort will be required to construct AOPs for exposures to different chemical groups making sure that we have enough representation of different test species to adequately cover the tree of life. This should include plants, which have not yet received sufficient attention from the AOP community. In this chapter, we present Chlamydomonas reinhardtii, a unicellular green microalga that serves as a model organism for, among others, photosynthesis and the circadian rhythm. We review C. reinhardtii as a model organism for ecotoxicology and summarize different publicly available genomic and OMICS resources for the species. We also present a new putative AOP for C. reinhardtii exposed to silver, constructed based on integration of transcriptomic and proteomic datasets. Finally, we present the current state-of-the-art bioinformatics procedures that can be used for constructing AOPs from OMICS type of datasets and evaluate whether the approaches are suitable for C. reinhardtii.

Biofilms causing medical conditions or interfering with technical applications can prove undesirably resistant to silver nanoparticle (AgNP)-based antimicrobial treatment, whereas beneficial biofilms may be adversely affected by the released silver nanoparticles. Isolated biofilm matrices can induce reduction of silver ions and stabilization of the formed nanosilver, thus altering the exposure conditions. We thus study the reduction of silver nitrate solution in model experiments under chemically defined conditions as well as in stream biofilms. Formed silver nanoparticles are characterized by state-of-the art methods. We find that isolated biopolymer fractions of biofilm organic matrix are capable of reducing ionic Ag, whereas other isolated fractions are not, meaning that biopolymer fractions contain both reducing agent and nucleation seed sites. In all of the investigated systems, we find that silver nanoparticle–biopolymer interface is dominated by carboxylate functional groups. This suggests that the mechanism of nanoparticle formation is of general nature. Moreover, we find that glucose concentration within the biofilm organic matrix correlates strongly with the nanoparticle formation rate. We propose a simple mechanistic explanation based on earlier literature and the experimental findings. The observed generality of the extracellular polymeric substance/AgNP system could be used to improve the understanding of impact of Ag+ on aqueous ecosystems, and consequently, to develop biofilm-specific medicines and bio-inspired water decontaminants.